1. Field of the Invention
This invention relates generally to the field of heat-resistant polymers with dielectric properties. More particularly, it relates to diamines and polymers containing three ether-linked benzonitrile moieties, polymers made therefrom, and methods of making the same.
2. Description of the Related Art
Materials with a high dielectric constant or relative permittivity (K) have recently received increasing interest for various potential applications including high energy-density-storage capacitor, gate dielectrics, and electroactive materials. In particular, materials with a high dielectric constant and low dielectric loss are critical for the applications of embedded passives such as capacitors. Such materials are one of the enabling technologies for microelectronic-system integration to provide the necessary size reduction without compromising the performance, and in some cases, with the possibility of performance enhancement in electronic systems. For capacitor applications, materials should generally possess the following properties: high dielectric constant, low dissipation factor, high thermal stability, simple processability, and good dielectric properties over a broad frequency range.
However, it is has also become clear that no single material would be able to satisfy all of these prerequisites. Therefore, recent years have witnessed an extensive exploitation of polymer-nanocomposites strategy. The overarching goal of these efforts is to combine the best characteristics of nano-fillers and matrix polymers in a synergistic fashion to improve the dielectric performance of the materials in terms of maximizing the dielectric constant and at the same time, managing the dielectric loss to an acceptable level. From the materials standpoint, there is clearly an increasing need for high-K, non-conducting polymers (i.e. devoid of both intrinsically electronic and ionic conduction) that are processable and compatible with high-K nanoparticles.
With the exception of ferroelectric polymers such as poly(vinylidene fluoride, PVDF (K-values of 9-10) and poly(vinylidene-fluoride-trifluoroethylene) or P(VDF-TrFE)-based, high-K fluoroterpolymers (K>60), the dielectric constant values for organic and nonferroelectric polymers are typically in the 2-4 range. However, the low surface energy of these highly fluorinated polymers makes them poor matrix materials for both carbon-based and inorganic nano-fillers because of the inherent interfacial incompatibility between them. In addition, the useful dielectric properties of these highly fluorinated polymers are generally stable only at temperatures below 125° C.
To increase the dielectric constant property of polymers, one approach that has been explored is to raise the polarity of the molecular chain by introducing highly neutral or zwitterionic polar groups into the side chains. Thus, for flexible aliphatic polymers, namely poly(olefins) and polysiloxanes, highly polar pendants such as cyclic sulfoxide and carbonate, as well as zwitterionic moieties such as pyridium-propanesulfonate and imidazolium-propanesulfonate, have been attached to polymer backbones. The dielectric properties were improved but generally with limited success. For example, cyclic carbonate-containing PMMA appeared to have the best performance: 6.0 (1 KHz), 5.0 (1 MHz), and 3.4 (1 GHz) with dielectric loss of 0.1-0.2 in the testing range of 1 MHz-1 GHz, where the relatively large loss is ascribed to the association of the zwitterionic units under the influence of electric field.
In the case of less flexible, aromatic polyimides, hole-transporting triphenylamine units have been incorporated into the polymer backbone, resulting in dielectric constants (3.57-4.93 at 1 kHz) higher than those of common polyimides (e.g. Kapton® film, DuPont™, with a value of 3.2). Similarly, the aryl-substituted pyridine heterocylic ring and nitrile (—CN) group were found to be effective in raising the K value up to 4.5 at 1 KHz. While no dielectric loss data is reported for these polymers, substantial dielectric loss has been reported for (βCN)APB-ODA, a non-fluorinated polyimide, at temperatures around 150° C. Therefore, mechanically and thermally robust polymer dielectrics are needed to increase the operating temperature range and to mitigate thermal management issues in compact pulsed power applications.